1. Field of the Invention
The present invention relates to a light control film used for backlight units such as those for liquid crystal displays and so forth, and a backlight unit using the same.
2. Description of Related Art
For liquid crystal displays and so forth, backlight units of the edge light type or direct type are conventionally used. Since backlight units of the edge light type can be manufactured with a small thickness, they are used for notebook computers etc., whereas backlight units of the direct type are used for large-sized liquid crystal television, etc.
Light emitted from these conventional backlight units includes components projected along directions significantly inclined from the front direction. Light emitted from backlight units of the edge light type, in particular, contains a lot of components projected along directions significantly inclined from the front direction, and thus it is difficult to obtain high front luminance.
In the conventional backlight units, two or more optical films such as prism sheets and light diffusive films are used in combination in order to improve front luminance so that the light is directed to the front. See, for example, claim 1 and [0034] of Japanese Kokai 9-127314.
Although prism sheets can generally increase the ratio of light emerging in the front direction (the direction perpendicular to the film surface) by surface design based on geometric optics. However, they have drawbacks in that they are likely to create an interference pattern due to regularly arranged convex portions, and in that they cause glare if they are used alone and thus they impair visibility of the image. Moreover, they unduly concentrate light in the front direction, and therefore they cannot provide a wide viewing angle.
On the other hand, if diffusion films are used alone, the front luminance becomes insufficient, although the aforementioned problems are avoided.
In the technique disclosed in Japanese Kokai 9-127314, a prism sheet and a light diffusive film are used in combination. However, the front luminance enhanced by the prism sheet is reduced by the use of the light diffusive film. Moreover, the films in layers may create Newton rings between the layers. Further, scratches and so forth may be caused by the contact of the films.